1. Field of the Invention
The present invention relates to a positioning apparatus, and in particular, though not exclusively, to a positioning apparatus used in an exposure apparatus and/or survey equipment.
2. Description of the Related Art
A conventional exposure apparatus can have a positioning apparatus for positioning a wafer or a reticle. Japanese Patent Laid-Open No. 2004-254489 discusses a stage unit using a surface motor, as a wafer stage, for positioning a wafer.
FIG. 8A illustrates a top view which shows the wafer stage 8 discussed in Japanese Patent Laid-Open No. 2004-254489, and FIG. 8B illustrates a sectional view which shows the wafer stage 8 as viewed sidewise.
Referring to these figures, a movable member 1 (stage) includes a magnet unit 2 in which permanent magnets are arranged in the so-called Halbach array at its bottom surface, and a base member 3, which has a coil unit 4 in which a plurality of coils are arranged. Magnetic fluxes generated from these permanent magnets and currents fed to the coils produce a Lorentz's force by which the movable member 1 is displaced.
FIGS. 9A to 9B illustrate views which show a configuration of coils and permanent magnets discussed in the Japanese Patent Laid-Open No. 2004-254489, as viewed from above in FIGS. 8A and 8B, and in which the stage is shown being see-through in order to facilitate the understanding of the configuration thereof. A plurality of coils 5 having linear portions in the X-axial direction are arranged in the Y-axial direction, and current having predetermined phases are fed to those of the coils 5 which are located underneath the magnets so as to displace the stage in the Y-axial direction. Further, with the provision of a plurality of coils having linear portions in the Y-axial direction, which are arranged in the X-axial direction, the stage can be displaced in the X-axial direction. It is noted here that the magnet unit 2 has such a magnetic configuration that the Halbach array has deficient parts 6 from which permanent magnets are in part removed as shown in FIG. 9A, or the Halbach array has additional parts in which permanent magnets are in part added 7 as shown in FIG. 9B. With this magnet configuration, currents are fed to coils underneath a pair of deficient parts 6 or additional parts 7 so as to induce forces in reverse direction, respectively therefrom, so as to cause the stage 1 to displace in the θz direction (a rotational direction around the Z-axis).
As illustrated in FIG. 9A, if defective portions are provided in permanent magnets having an array sequence, permanent magnets used for X- and Y-axial displacements can be removed, resulting in decreased drive efficiency. As illustrated in FIG. 9B, if additional portions are provided in permanent magnets having an array sequence, separates coils for θz drive can be used in addition to coils for X- and Y-axial drives in order to increase efficiency of the drive. In this case, since a current applied for the θz drive is different from currents applied for the X- or Y-axial drive, different current drives can be used, that is, an increase in the number of current drivers results in increased costs. Further, since the additional magnets overhang outward by a large degree, the stage itself would have a larger size, the larger the carriage, the larger the apparatus and as well the larger the heating value of a drive unit, resulting in difficulty in maintaining increased accuracy.